Density functionals in the presence of magnetic field

In this article, density functionals for Coulomb systems subjected to electric and magnetic fields are developed. The density functionals depend on the particle density ρ and paramagnetic current density j^p. This approach is motivated by an adapted version of the Vignale and Rasolt formulation of current density functional theory, which establishes a one‐to‐one correspondence between the nondegenerate ground‐state and the particle and paramagnetic current density. Definition of N‐representable density pairs (ρ,j^p) is given and it is proven that the set of v‐representable densities constitutes a proper subset of the set of N‐representable densities. For a Levy–Lieb‐type functional Q(ρ,j^p), it is demonstrated that (i) it is a proper extension of the universal Hohenberg–Kohn functional to N‐representable densities, (ii) there exists a wavefunction ψ₀ such that , where H₀ is the Hamiltonian without external potential terms, and (iii) it is not convex. Furthermore, a convex and universal functional F(ρ,j^p) is studied and proven to be equal the convex envelope of Q(ρ,j^p). For both Q and F, we give upper and lower bounds. © 2014 Wiley Periodicals, Inc.     

Hohenberg–Kohn theorems in the presence of magnetic field

In this article, we examine Hohenberg–Kohn theorems for Current Density Functional Theory, that is, generalizations of the classical Hohenberg–Kohn theorem that includes both electric and magnetic fields. In the Vignale and Rasolt formulation (Vignale and Rasolt, Phys. Rev. Lett. 1987, 59, 2360), which uses the paramagnetic current density, we address the issue of degenerate ground states and prove that the ensemble‐representable particle and paramagnetic current density determine the degenerate ground states. For the formulation that uses the total current density, we note that the proof suggested by Diener (Diener, J. Phys.: Condens. Matter. 1991, 3, 9417) is unfortunately not correct. Furthermore, we give a proof that the magnetic field and the ensemble‐representable particle density determine the scalar and vector potentials up to a gauge transformation. This generalizes the result of Grayce and Harris (Grayce and Harris, Phys. Rev. A 1994, 50, 3089) to the case of degenerate ground states. We moreover prove the existence of a positive wavefunction that is the ground state of infinitely many different Hamiltonians. © 2014 Wiley Periodicals, Inc.     

Electrodeposition of white gold alloys: an electrochemical,spectroelectrochemical and structural study of the electrodeposition of Au-Sn alloys in the presence of 4-cyanopyridine

A bath for the electrodeposition of Au-Sn alloys is proposed and the properties of the deposit obtained have been studied, in view of applications in the field of white precious metal plating and electroforming. 4-Cyanopyridine has been employed as an organic additive to confer stability to the bath and compactness to the deposit. The electrochemical behaviour of the bath has been investigated by means of cyclic voltammetry, stripping potentiodynamic scans, open circuit potential decay measurements and potentiostatic transients. The nucleation behaviour of the system has been studied on glassy carbon electrodes. The electrodic behaviour of 4-cyanopyridine was investigated as a function of electrode potential by in situ Raman spectroscopy. The composition of the alloys was evaluated by electron dispersive spectroscopy, the crystalline structure by X-ray diffraction and the morphology by scanning electron microscopy. The effects of the additive on the crystalline structure and on the morphology of the electrodeposits have been highlighted. Potential-dependent adsorption, reorientation and cathodic reactivity of 4-cyanopyridine during the alloy electrodeposition process have been assessed.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany     

Electrodeposition of rhenium and its alloys

The processes of electrodeposition of rhenium and its alloys with nickel from aqueous solutions are considered. The results of theoretical and experimental studies of the process of perrhenate ion reduction are analyzed: the data on the possible mechanisms of the cathodic process, participation of atomic hydrogen in it, potentials of transition of rhenium to different oxidation degrees. Codeposition of rhenium and nickel is discussed. The effect of complexation on the current efficiency of rhenium deposition is considered. Information of the sources of data discussed in this paper is provided.     

Molecular polarization and laser photopredissociation in the presence of a magnetic field

The theory of the angular distribution of the photofragment resulting from weak predissociation in a diatomic molecule is worked out in the density matrix formalism. Special attention is given to the relationship between photofragment anisotropy, molecular polarization and fluorescence light polarization. The effect of a steady applied magnetic field is discussed and compared with classical Hanle effect. Application to the case of O₂⁺, b⁴σ_R^? state studied by fast ion beam laser spectroscopy (FIBLAS) is presented. Zeeman effect of the low J levels is observed in good agreement with theory and the angular distribution of the photofragments arising from a few selected Zeeman sublevels offers qualitative experimental confirmation of the theoretically predicted behavior.     

Electrodeposition of manganese dioxide: effect of quaternary amines

The effect of quaternary ammonium salts (tetraethyl ammonium bromide, tetrapropyl ammonium bromide, and tetrabutyl ammonium bromide) on the structural, morphological, and electrochemical characteristics of electrolytic manganese dioxide (EMD) obtained from acidic aqueous sulfate solution has been investigated. Physical characterization of the EMD was achieved by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, differential thermal analysis, and Fourier transform infrared spectroscopy. The charge–discharge profile of the materials was determined to evaluate their potential for alkaline battery applications. The presence of these quaternary ammonium salts as organic additives in the solution increased the current efficiency while decreasing energy consumption during electrochemical deposition of manganese dioxide (MnO₂). All the additives influenced the discharge characteristics of the EMD samples significantly, producing a cathode material with increased cumulative discharge capacity relative to EMD prepared in the absence of additives. This is attributed to the ability of the additives to affect the particle size and morphology, and therefore electrochemical activity, of electrodeposited materials; the effects in the case of the additives investigated in this work were positive, producing a material with potential application to battery technology.     

Dynamic response of a unijunction transistor in the presence of a magnetic field

The influence of a magnetic field on the small-signal dynamic response of a unijunction transistor (UJT) and the performance of a UJT sine-wave oscillator in the presence of an externally applied magnetic field are discussed. A theoretical analysis of the magnetically-induced changes in differential negative resistance and inductance (which describe the dynamic response of a UJT) is proposed for low frequencies. The change in differential negative resistance and inductance due to a magnetic field has been attributed to the corresponding change in basic electrophysical parameters (carrier mobility and carrier lifetime) of the device under investigation. This theoretical analysis has been experimentally verified. Subsequently, these results have been used in a study of magnetically-induced changes in the amplitude and frequency of a UJT sine-wave oscillator. This study suggests its possible application as a magnetic transducer.     

Liquid crystal electrohydrodynamics in the presence of a magnetic field: the dynamic scattering transition

We have studied electrohydrodynamic convection in the nematic liquid crystal MMBA in the conduction regime in the presence of a competing magnetic field. This field substantially alters the behaviour of the system, causing a metastable surface deformation and travelling waves. The magnetic field also alters the transition between the two dynamic scattering modes so that both states retain anisotropic ordering. A scaling relation is found describing this hysteretic transition. We report the existence of a stable mixed state of DSM 1 and DSM 2.     

Liquid crystal electrohydrodynamics in the presence of a magnetic field: the dynamic scattering transition

We have studied electrohydrodynamic convection in the nematic liquid crystal MMBA in the conduction regime in the presence of a competing magnetic field. This field substantially alters the behaviour of the system, causing a metastable surface deformation and travelling waves. The magnetic field also alters the transition between the two dynamic scattering modes so that both states retain anisotropic ordering. A scaling relation is found describing this hysteretic transition. We report the existence of a stable mixed state of DSM 1 and DSM 2.     

Singlet—triplet radiationless processes in glyoxal in the presence of a magnetic field

The magnetic quenching of fluorescence in glyoxal is studied under the single-rotational level excitation. It is shown that the magnetic effect saturates in the fields inducing a complete spin—rotation decoupling evidenced in a study of the Zeeman effect in the ³A_u ← ¹A_u transition. The increase of the collision-induced intersystem crossing rate k_ISC may be accounted for by a magnetic mixing of triplet sublevels (only partially mixed by rotation) in the specific case, of a non-linear dependence of k_ISC on the singlet—triplet mixing coefficients.     

Mixed convection characteristics in a baffled U-shaped lid-driven cavity in the presence of magnetic field

Journal of Thermal Analysis and Calorimetry - The lattice Boltzmann method is utilized to investigate the mixed convection of a CuO/water nanofluid by magnetic field’s effect in a lid-driven...     

Synthesis and characterization of polyaniline nanoparticles in the presence of magnetic field and samarium chloride

A new and economical method of preparing polyaniline (PANI) nanoparticles will be introduced in this article. Compared with conventional methods, this method is much more simple and convenient. Scanning electron microscope (SEM) shows that the diameter of particles are between 30 and 50 nm, which is in good agreement with the results of a transmission electron microscope (TEM). Polyaniline/SmCl₃/Bp, polyaniline/SmCl₃ and polyaniline/HCl were prepared in a solution containing 1.0 mol dm⁻³ aniline, 1.0 mol dm⁻³ HCl with and without 0.5 mol dm⁻³ SmCl₃, in the presence and in the absence of a magnetic field, respectively. Their conductivity, UV-vis spectra, FTIR spectra, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were investigated. Changes in UV-vis and FTIR spectra indicate a strong interaction between Samarium ions (SmCl₃) and polyaniline chains. The conductivity of PANI depends on magnetization and concentration of Sm³⁺. Polyaniline/SmCl₃/Bp has the higher degree of crystallinity than that of polyaniline/HCl.     

Reactivity dynamics of a confined molecule in presence of an external magnetic field

Reactivity dynamics and stability of a confined hydrogen molecule in presence of an external magnetic field has been studied using quantum fluid density functional theory. Dynamic profiles of various reactivity parameters such as hardness, electrophilicity, magnetizability, phase volume, entropy, etc. have been studied within a confined environment. Responses in the reactivity parameters as well as the associated electronic structure principles validate the stability of the confined H₂ molecule in ground and excited states in presence of an external magnetic field. Confinement to the system has been imposed by the Dirichlet type boundary condition. Confinement and excitation act in opposite directions. Ground state type dynamics is obtained on simultaneous electronic excitation and confinement. © 2014 Wiley Periodicals, Inc.     

Electrodeposition of highly alloyed quaternary PtPdRuOs catalyst with highly ordered nanostructure

Introducing palladium to traditional platinum-based alloy electrocatalysts offers a novel approach to develop highly efficient anode electrocatalysts for direct methanol fuel cells. In this communication, we report the preparation of thin-wall mesoporous quaternary PtPdRuOs alloy catalyst via electrochemical co-reduction of their chloride precursors all dissolved in aqueous domains of the liquid crystalline phases of an oligoethylene oxide surfactant. Scanning electron micrographs (SEM) reveal that the deposit is composed of uniform nanospheres with an average diameter of around 120 nm and the average mole composition of the metal elements is Pt₃₇Pd₃₃Ru₂₂Os₁₀. Transmission electron micrographs (TEM) disclose that the nanospheres have an ordered nanostructure which is characterized by periodic pores of 3.6 ± 0.4 nm in diameter separated by walls of 2.4 ± 0.4 nm in thickness. X-ray diffraction studies signal a highly alloying degree for the four metal components in the deposit. The specific electrochemical surface area of the nanostructured powder assessed using underpotential deposited Cu stripping technique is as high as 105 m² g^–1, much higher than that of unsupported precious metal catalysts prepared using standard techniques. These characters suggest that the quaternary PtPdRuOs alloy materials with high surface area and thin-wall mesoporous structure would be a novel class of promising electrocatalysts for direct methanol fuel cells.     

Electrodeposition of iron from sulfate solutions in the presence of aminoacetic acid

The kinetics and technology of iron electrodeposition from sulfate solutions containing various amounts of aminoacetic acid at pH 1.65, 1.95, and 2.50 in the temperature range 20–50°C were studied.     

Electrodeposition of nickel from sulfate solutions in the presence of aminoacetic acid

Kinetics of nickel electrodeposition from sulfate electrolytes in the presence of aminoacetic acid at pH of 2.0 and 5.5 in the temperature range 20–50°C is considered.     

Formation of walls in cylindrical smectic C layers in the presence of a tilted magnetic field

A theoretical study of the elastic properties of a smectic C liquid-crystalline system consisting of cylindrical smectic layers is presented. We show that the ground state configuration of the c-director for such a system depends on the signs of two combinations of the relevant elastic constants. With these configurations as a starting point, we describe how a set of walls under certain conditions must be formed in the system if a magnetic field is applied at an angle to the cylinder axis. An estimate of the thickness of these walls is given. We also show that, depending on whether the angle between the magnetic field and the cylinder axis is larger or smaller than the tilt of the director with respect to the smectic layer normal, the system will exhibit two qualitatively different behaviours.     

Electrodeposition of copper in the presence of an acoustically excited gas bubble

Copper has been electrodeposited in the presence of an acoustically excited gas bubble (Ar bubbles with radii ∼1.5 mm held below a copper plate). Under the conditions employed, an acoustic pressure amplitude of 69.5 Pa is sufficient to excite multiple surface wave modes on the bubble wall. This is observed using high-speed imaging. This oscillation generates significant micromixing, which brings fresh electrolyte to the electrode surface leading to an enhanced deposition current. Scanning electron microscopy reveals radial streaming patterns in the resulting copper deposit. Experiments carried out using a lower acoustic pressure amplitude of 50.5 Pa (such that only the Faraday wave is excited) exhibit a lesser degree of streaming and mass transfer enhancement. No significant spatially averaged current enhancement is seen if the bubble is only undergoing breathing mode oscillation.     

Density of electron states in crystalline systems calculated in the presence and absence of the magnetic field

It is demonstrated in terms of explicit calculations that the average density of states in a crystalline system remains unaffected by the presence of the external magnetic field. This is so on condition the magnetic field is weak enough to provide us with a large number of the Landau levels per energy unit. For a special case of a two‐dimensional crystalline system, the equivalence of the density of states obtained in the presence and the absence of the magnetic field can be shown in an analytic way. For three dimensions, the tightly bound s‐electron states in crystals having cubic symmetry are taken into consideration. Here the density of states calculated in the presence of the magnetic field is compared numerically with that of the field‐absent Bloch states acquired with the aid of Jelitto's method. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Electrodeposition of Zn–Ni alloys from sulfate bath

The electrodeposition of zinc–nickel (Zn–Ni) alloys from sulfate baths has been studied at different deposition times and H₂SO₄ and NiSO₄ concentrations; various characteristics have been observed during alloy deposition and dissolution. The deposit has been investigated by using scanning electron microscopy (SEM) and X-ray diffractometry. Cyclic voltammetry and galvanostatic measurements during electrodeposition have been conducted. Electrochemical and surface analysis indicate that deposition takes place with the formation of two different structures corresponding to γ-phase and δ-phase zinc–nickel alloys. During anodic part of the cyclic voltammetry of the alloys, a reduction process has been observed, which may be due to hydrogen evolution. With the increase of nickel concentration in the bath, the amount of γ-phase increases, as indicated by the relative increase in the height of the peaks in the X-ray patterns and anodic peaks in the cyclic voltammograms. Also, the corrosion resistance of the zinc–nickel alloy has been improved with an increased concentration of nickel. Under these experimental conditions the electrodeposition of the alloys is of anomalous type.